Resin bonding method by photoirradiation, method for producing resin article, resin article produced by the same method, method for producing microchip, and microchip produced by the same method

ABSTRACT

A resin bonding method according to the present invention is a resin bonding method for bonding a first resin and a second resin including (I) a step of irradiating spaces containing oxygen molecules with vacuum ultraviolet light having a wavelength of 175 nm or less, the spaces being in contact with surfaces of the first and second resins; and (II) a step of, after the irradiation, subjecting the surfaces to temperature rise while the surfaces are in contact with each other, to bond the first resin and the second resin together with the surfaces serving as bonding surfaces. In the step (I), the surfaces of the first and second resins may be further irradiated with the vacuum ultraviolet light. In this case, a light amount of the vacuum ultraviolet light having reached the surfaces is preferably, for example, 0.1 J/cm 2  or more and 10 J/cm 2  or less.

CLAIM OF PRIORITY

This application is a Divisional of U.S. application Ser. No. 12/823,088filed on Jun. 24, 2010 which is a Continuation of InternationalApplication No. PCT/JP2008/073703 filed on Dec. 26, 2008, which claimsbenefit of Japanese Patent Application No. 2007-337411 filed on Dec. 27,2007, all of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a resin bonding method by irradiationwith light (vacuum ultraviolet light); and a method for producing aresin article and a method for producing a microchip in which the resinbonding method is employed. The present invention further relates to aresin article and a microchip produced by such methods.

2. Description of the Related Art

In general, a method for bonding resins is performed by bonding bythermal fusion or bonding by coating an organic solvent or an adhesive.Bonding by thermal fusion is generally performed at the glass transitiontemperatures of resins or higher.

Microchips typically having a structure in which a pair of substratesare bonded together so as to face each other, at least one of thesubstrates including a microchannel in a surface, have been attractingattention. Microchips are also referred to as micro-fluid devices.

In microchips, by providing regions having various functions such as areaction region where a reagent is placed in channels also referred toas microchannels, chips suitable for various applications can beprovided. Microchips are typically applied to analyses such as geneanalyses, clinical diagnosis, and drug screening in the fields ofchemistry, biochemistry, pharmacy, medicine, and veterinary medicine;synthesis of compounds; environmental measurements; and the like. Whenmicrochips are used for such applications, for example, compared withthe cases where existing analytical instruments suitable for similarapplications are used, the following advantages can be provided: forexample, (1) the amounts of a sample and a reagent necessary for ananalysis can be reduced; (2) analysis time can be reduced; and (3) chipsare disposable and hence safety and measurement accuracy can be enhancedin the field of medicine and the like.

Microchips have been mainly formed of glass substrates because glasssubstrates are easy to produce and allow optical detection. However,microchips formed of glass substrates are likely to be damaged byexternal impacts and the weight of such microchips is problematic upontransportation, disposal, and the like. Accordingly, developments ofmicrochips formed of resin substrates that are lightweight but lesslikely to be damaged and inexpensive compared with glass substrates havebeen performed.

In microchips formed of resin substrates, a method for bonding the resinsubstrates together is important.

To bond resin substrates together, a general method for bonding resinssuch as thermal fusion can be employed. However, since bonding bythermal fusion is generally performed at the glass transitiontemperatures of resins or higher, there are cases where substratesdeform upon bonding and the resultant microchips do not function. Inaddition, since the influence of deformation of substrates becomessevere when the width of channels is decreased or the pattern ofchannels is made complicated, it is difficult to make microchips highlyfunctional by bonding performed by thermal fusion.

Deformation of resin substrates can be suppressed by bonding at lowertemperature. As such a bonding method, Japanese Unexamined PatentApplication Publication No. 2005-80569 discloses a microchip joiningmethod in which a portion having no channels in a substrate havingmicrochannels in a surface is coated with an organic solvent and thesubstrate is then placed on a substrate having a flat surface and thesesubstrates are fused together.

Japanese Unexamined Patent Application Publication No. 2005-257283discloses a microchip production method in which a polydimethylsiloxane(PDMS) substrate and a resin substrate (counter substrate) composed of amaterial other than PDMS are bonded together. In this production method,a PDMS substrate in a surface of which microchannels are formed and acounter substrate on a surface of which a silicon oxide film is formedare prepared. After the bonding surfaces of the substrates are subjectedto a modification treatment, the substrates are bonded together with thesilicon oxide film therebetween. A described example of such amodification treatment for bonding surfaces is an oxygen plasmatreatment, specifically, an oxygen plasma treatment in which irradiationwith excimer ultraviolet light in an oxygen atmosphere is performed (forexample, paragraph [0017] of Japanese Unexamined Patent ApplicationPublication No. 2005-257283).

Although the following is not directly related to microchip productionmethods, Japanese Unexamined Patent Application Publication Nos.2005-171164 and 2004-43662 disclose a method in which surfaces of olefinresins are irradiated with light to activate the surfaces (in JapaneseUnexamined Patent Application Publication No. 2005-171164, aphotopolymerizable resin for surface modification is also used), theactivated surfaces are coated with a resin composition such as ahot-melt adhesive or an ultraviolet curable resin, and the resins arebonded together with the composition therebetween.

SUMMARY OF THE INVENTION

In the method according to Japanese Unexamined Patent ApplicationPublication No. 2005-80569, an organic solvent is coated so as to avoidchannels since entry of an organic solvent into channels causes erosion,alteration, or the like of resins forming substrates, which can causeclogging of channels, degradation of characteristics of microchips, orthe like. However, such a coating step of an organic solvent can degradeproductivity of microchips. In addition, in the production of microchipsin which the width of channels is decreased or the pattern of channelsis made complicated for the purpose of making microchips highlyfunctional or the like, it is difficult to apply such a coating step ofan organic solvent depending on the degree of the decrease or thecomplication.

In the method according to Japanese Unexamined Patent ApplicationPublication No. 2005-257283, since organic solvents or adhesives are notused, clogging of channels, degradation of characteristics ofmicrochips, or the like is less likely to be caused, compared with themethod according to Japanese Unexamined Patent Application PublicationNo. 2005-80569. However, the method according to Japanese UnexaminedPatent Application Publication No. 2005-257283 is used only for bondingbetween a silicon oxide film and a substrate of PDMS, which is asilicone resin including Si—O bonds and has a high affinity for asilicon oxide film. Thus, the method is not used for bonding togetherresin substrates other than PDMS substrates.

The methods according to Japanese Unexamined Patent ApplicationPublication Nos. 2005-171164 and 2004-43662 require coating of substratesurfaces with a resin composition, which causes clogging of channels orthe like. Accordingly, it is difficult to apply these methods withoutchange to methods for producing microchips. As in Japanese UnexaminedPatent Application Publication No. 2005-80569, a resin composition maybe coated so as to avoid channels. However, as described above, such acoating step can degrade productivity of microchips. In addition, whenthe width of channels is decreased or the pattern of channels is madecomplicated, it is difficult to apply such a coating step.

In summary, when microchips are produced, a resin bonding method isdemanded by which resin substrates can be bonded together at atemperature lower than that in bonding by thermal fusion, withoutperforming coating of organic solvents or resin compositions, whichdegrades the productivity of the chips and can cause clogging ofchannels or the like. In addition, such a bonding method is expected tobe applied to production methods not only for microchips but also forvarious resin articles.

A resin bonding method according to the present invention is a resinbonding method for bonding a first resin and a second resin togetherincluding: (I) a step of irradiating spaces containing oxygen moleculeswith vacuum ultraviolet light having a wavelength of 175 nm or less, thespaces being in contact with surfaces of the first and second resins;and

(II) a step of, after the irradiation, subjecting the surfaces totemperature rise while the surfaces are in contact with each other, tobond the first resin and the second resin together with the surfacesserving as bonding surfaces.

Note that, in the step (I) of a resin bonding method according to thepresent invention, the spaces being in contact with surfaces of thefirst and second resins are spaces immediately above the surfaces of thefirst and second resins. The spaces are preferably spaces within 0 to 30mm from the surfaces, more preferably, spaces within 0 to 1 mm from thesurfaces.

A bonding method according to the present invention can be applied to amethod for producing a resin article including a portion in which aresin and a resin are bonded together. That is, a method for producing aresin article according to the present invention is a method forproducing a resin article including two or more parts including resinportions, the two or more parts being bonded together through the resinportions, wherein the resin portions are bonded together by theabove-described bonding method according to the present invention.

In addition, the present invention provides a resin article produced bythe above-described method for producing a resin article according tothe present invention. A resin article according to the presentinvention is a resin article produced by the above-described method forproducing a resin article according to the present invention, whereinthe resin portions of the two or more parts are bonded together suchthat the resin portions can be separated from each other by using atleast one liquid at 40° C. or more selected from water and alcohol or byusing a liquid less than 40° C. and ultrasonic vibrations.

A method for producing a resin article according to the presentinvention can be applied to methods for producing various resinarticles, for example, microchips. That is, a method for producing amicrochip according to the present invention is a method for producing amicrochip including a pair of resin substrates bonded together so as toface each other, at least one of the resin substrates including achannel, wherein the resin substrates are bonded together by theabove-described bonding method according to the present invention.

In addition, the present invention also provides a microchip produced bythe above-described method for producing a microchip according to thepresent invention. A microchip according to the present invention is amicrochip produced by the above-described method for producing amicrochip according to the present invention, wherein the pair of resinsubstrates are bonded together such that the pair of resin substratescan be separated from each other by using at least one liquid at 40° C.or more selected from water and alcohol or by using a liquid less than40° C. and ultrasonic vibrations.

The present invention also provides a resin bonding method for bonding afirst resin and a second resin together including: (III) a step ofirradiating spaces containing oxygen molecules with vacuum ultravioletlight having a wavelength of 175 nm or less, the spaces being in contactwith surfaces of the first and second resins; and

(IV) a step of, after the irradiation, subjecting the surfaces totemperature rise while the surfaces are in contact with each other, tobond the first resin and the second resin together with the surfacesserving as bonding surfaces,

wherein, in the step (III), irregularities are formed in the surfaces ofthe first and second resins, the surfaces serving as the bondingsurfaces; and, in the step (IV), the surfaces of the first and secondresins are bonded together.

When a bonding method according to the present invention is employed, aresin and a resin can be bonded together with high productivity at atemperature lower than that in bonding by thermal fusion, withoutperforming coating of organic solvents or resin compositions. Inaddition, resins having been bonded together by such a method can bereadily separated from each other at the bonding surfaces by using aliquid such as water at 40° C. or more or by using a liquid less than40° C. and ultrasonic vibrations. Accordingly, for example, a resinarticle formed by bonding together resin parts (parts including resinportions) by such a bonding method can be readily disassembled into theparts after use by immersing the resin article into hot water or thelike. Thus, when a bonding method according to the present invention isemployed, recycling of resin parts is facilitated.

When such a bonding method is applied to a method for producing a resinarticle, that is, in a method for producing a resin article according tothe present invention, various advantages can be provided depending onthe type of the article. In addition, since a resin article according tothe present invention produced by such a production method hassufficiently high bonding strength between parts, the article hasreliability. Furthermore, since such an article can also be readilydisassembled into parts, recycling of parts is also possible.

When a bonding method according to the present invention is applied to amethod for producing a microchip, that is, in a method for producing amicrochip according to the present invention, a pair of resin substratesin at least one of which a channel is formed can be bonded together at atemperature lower than that in bonding by thermal fusion. Thus,deformation of the resin substrates upon the bonding can be suppressed.In addition, since coating of the bonding surfaces of substrates with anorganic solvent or a resin composition is not necessary, the productionmethod can be performed at high productivity; clogging of channels anddegradation of characteristics of microchips can be suppressed duringproduction; and, in addition, such a method can be more readily appliedwhen the width of channels is decreased or the pattern of channels ismade complicated. In addition, a microchip according to the presentinvention produced by such a production method has a sufficiently highbonding strength between resin substrates and hence the microchip hasreliability. Furthermore, since such a microchip can also be readilydisassembled into resin substrates, recycling of resin substrates isalso possible.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a process diagram schematically illustrating a bonding methodaccording to an embodiment of the present invention;

FIG. 1B is a process diagram schematically illustrating a bonding methodaccording to an embodiment of the present invention;

FIG. 2 illustrates results obtained by measuring with a Fouriertransform infrared spectrophotometer the state of irradiated surfaces ofresins having been irradiated with vacuum ultraviolet light having awavelength of 172 nm at an irradiation distance of 5 mm;

FIG. 3 illustrates results obtained by measuring with a Fouriertransform infrared spectrophotometer the state of irradiated surfaces ofresins having been irradiated with vacuum ultraviolet light having awavelength of 172 nm at an irradiation distance of 30 mm;

FIG. 4A illustrates results obtained by measuring by X-ray-inducedphotoelectron spectroscopy the state of an irradiated surface of a resinhaving been irradiated with vacuum ultraviolet light having a wavelengthof 172 nm at an irradiation distance of 5 mm;

FIG. 4B illustrates results obtained by measuring by X-ray-inducedphotoelectron spectroscopy the state of an irradiated surface of a resinhaving been irradiated with vacuum ultraviolet light having a wavelengthof 172 nm at an irradiation distance of 5 mm;

FIG. 5A illustrates results obtained by measuring by X-ray-inducedphotoelectron spectroscopy the state of an irradiated surface of a resinhaving been irradiated with vacuum ultraviolet light having a wavelengthof 172 nm at an irradiation distance of 30 mm;

FIG. 5B illustrates results obtained by measuring by X-ray-inducedphotoelectron spectroscopy the state of an irradiated surface of a resinhaving been irradiated with vacuum ultraviolet light having a wavelengthof 172 nm at an irradiation distance of 30 mm;

FIG. 6 is a schematic view illustrating a bonding method according to anembodiment of the present invention;

FIG. 7 is a schematic view illustrating a method for producing amicrochip according to an embodiment of the present invention;

FIG. 8 illustrates results of water contact angle obtained by measuringsubstrate surfaces in which the irradiation distance was made 5 mm andthe irradiation time were varied from 0 to 40 minutes;

FIG. 9 illustrates the ratio of oxygen atoms to carbon atoms calculatedfrom the measurement results by X-ray-induced photoelectron spectroscopyin terms of substrate surfaces in which the irradiation distance wasmade 5 mm and the irradiation time was varied from 0 to 40 minutes;

FIG. 10 illustrates results of water contact angle obtained by measuringsubstrate surfaces in which the irradiation distance was made 30 mm andthe irradiation time was varied from 0 to 40 minutes;

FIG. 11 illustrates the ratio of oxygen atoms to carbon atoms calculatedfrom the measurement results by X-ray-induced photoelectron spectroscopyin terms of substrate surfaces in which the irradiation distance wasmade 30 mm and the irradiation time was varied from 0 to 40 minutes;

FIG. 12 illustrates results of water contact angle obtained by measuringsubstrate surfaces in which the irradiation time was varied from 0 to 60minutes at humidity of 0.1% and 70%;

FIG. 13 illustrates the ratio of oxygen atoms to carbon atoms calculatedfrom the measurement results by X-ray-induced photoelectron spectroscopyin terms of substrate surfaces in which the irradiation time was variedfrom 0 to 60 minutes at humidity of 0.1% and 70%;

FIG. 14 illustrates results obtained by measuring with a Fouriertransform infrared spectrophotometer the state of irradiated surfaces ofresins having been irradiated with vacuum ultraviolet light in anatmosphere containing no oxygen molecules;

FIG. 15 illustrates results obtained by measuring by X-ray-inducedphotoelectron spectroscopy the state of irradiated surfaces of resinshaving been irradiated with vacuum ultraviolet light in an atmospherecontaining no oxygen molecules; and

FIG. 16 illustrates results obtained by measuring by X-ray-inducedphotoelectron spectroscopy the state of irradiated surfaces of resinshaving been irradiated with vacuum ultraviolet light in an atmospherecontaining no oxygen molecules.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A method for bonding resins according to the present invention will bedescribed.

In a bonding method according to the present invention, spacescontaining oxygen molecules are irradiated with vacuum ultraviolet lighthaving a wavelength of 175 nm or less, the spaces being in contact withsurfaces of the first and second resins (step (I)). Note that,hereafter, the surfaces of the first and second resins serving asbonding surfaces are sometimes simply referred to as “surfaces”.

In a bonding method according to the present invention, the surfaces ofthe first and second resins may be further irradiated with vacuumultraviolet light. That is, vacuum ultraviolet light may beappropriately adjusted in terms of irradiation intensity, irradiationdistance, or the like such that the vacuum ultraviolet light reaches thesurfaces of the first and second resins. By also irradiating thesurfaces of the first and second resins with vacuum ultraviolet light,the first resin and the second resin can be efficiently bonded together.Hereinafter, a bonding method according to the present invention will bedescribed with reference to drawings by using a case where spaces incontact with surfaces of the first and second resins and the surfacesare irradiated with vacuum ultraviolet light, the case serving as anexample.

As illustrated in FIG. 1A, spaces 10 in contact with surfaces 3 a and 3b of a first resin 1 and a second resin 2, the surfaces 3 a and 3 bserving as bonding surfaces, and the surfaces 3 a and 3 b are irradiatedwith vacuum ultraviolet light 4 having a wavelength of 175 nm or less(step (I)). The spaces 10 being in contact with the surfaces 3 a and 3 bcontain oxygen molecules. At this time, the light amount of the vacuumultraviolet light 4 radiated to the spaces 10 and the surfaces 3 a and 3b are not particularly restricted. However, by increasing the lightamount reaching the surfaces 3 a and 3 b, the first resin 1 and thesecond resin 2 can be efficiently bonded together in a short period oftime. Accordingly, to increase the amount of light reaching the surfaces3 a and 3 b, for example, the distance from a light source to thesurfaces 3 a and 3 b is desirably adjusted. Specifically, in the step(I), the irradiation intensity with the vacuum ultraviolet light 4, thedistance from a light source to the surfaces 3 a and 3 b, and theirradiation time are desirably appropriately adjusted such that thelight amount (hereafter, sometimes referred to as “reached lightamount”) of the vacuum ultraviolet light 4 reaching the surfaces 3 a and3 b is made 0.1 J/cm2 or more and 10 J/cm2 or less. Note that, thoughthe vacuum ultraviolet light 4 is radiated from the surfaces 3 a and 3 bsides in FIG. 1A, the radiation method is not particularly restricted tosuch a method. In a bonding method according to the present invention,at least the spaces 10 being in contact with the surfaces 3 a and 3 bshould be irradiated with the vacuum ultraviolet light 4. Accordingly,when the first and second resins are, for example, resin sheets ofpolyethylene having high transmissivity, the vacuum ultraviolet light 4may be radiated through surfaces opposite surfaces serving as bondingsurfaces.

After the step (I), as illustrated in FIG. 1B, the first resin 1 and thesecond resin 2 are bonded together with the surfaces 3 a and 3 b servingas bonding surfaces by subjecting the surfaces 3 a and 3 b totemperature rise while the surfaces 3 a and 3 b are in contact with eachother (step (II)).

The reason why the first resin and the second resin are bonded togetherby the steps (I) and (II) is not clear; however, possible reasons arethe following three phenomena.

First, the first phenomenon will be described. When the spacescontaining oxygen molecules and being in contact with surfaces of thefirst and second resins are irradiated with vacuum ultraviolet lighthaving a wavelength of 175 nm or less, the surface energy of thesurfaces of the first and second resins is increased (activated)compared with prior to the irradiation with vacuum ultraviolet light andoxygen-containing hydrophilic functional groups (hydrophilic functionalgroups containing oxygen atoms) such as hydroxyl groups, carbonylgroups, or carboxyl groups are generated on the surfaces. Then, bysubjecting the surfaces of the first and second resins to temperaturerise while the surfaces of the resins are in contact with each other,bonds of some kind using the functional groups are generated between thesurfaces of the first and second resins. Thus, the first resin and thesecond resin are probably bonded together with the surfaces serving asbonding surfaces.

For reference, when surfaces of a resin are irradiated with, forexample, vacuum ultraviolet light having a wavelength of 172 nm, theresults of measurement of the state of the surfaces with an FT-IR(Fourier transform infrared spectrophotometer) are illustrated in FIGS.2 and 3 and the results of measurement of the surfaces by X-ray-inducedphotoelectron spectroscopy (XPS) are illustrated in FIGS. 4A, 4B, 5A and5B. The resin used in these measurements was a cycloolefin polymer and alight source used was an excimer lamp. The irradiation intensity wasmade 10 mW/cm2. The distance from the light source to the surfaces ofthe resin was made 5 mm or 30 mm. The irradiation time was made 0minutes, 5 minutes, and 10 minutes. The results in the cases where theirradiation distance was 5 mm are illustrated in FIGS. 2, 4A, and 4B.The results in the cases where the irradiation distance was 30 mm areillustrated in FIGS. 3, 5A, and 5B. The results with the FT-IR show anincrease in the amount of O—H groups and C═O groups on the surfaces ofthe resin. In addition, the results by XPS show that, compared withprior to the irradiation with vacuum ultraviolet light, after theirradiation, signals from oxygen considerably increase in the O1sspectra; and in the C1s spectra, signals from carbon decrease andsignals (at about 290 eV in terms of binding energy) from carbon beingbonded to oxygen are newly observed. These results show thatoxygen-containing hydrophilic functional groups are probably generatedon the surfaces of the resin.

Here, the necessity of use of vacuum ultraviolet light having awavelength of 175 nm or less will be described. Note that vacuumultraviolet light generally refers to ultraviolet light having awavelength of 100 to 200 nm.

When oxygen molecules are excited with ultraviolet light, active oxygenspecies such as singlet oxygen atoms, triplet oxygen atoms, and ozonemolecules are generated. Oxidation of organic molecules caused by suchactive oxygen species probably promotes a surface treatment and bondingof resins. Singlet oxygen atoms are most oxidative against organicmolecules among the above-described active oxygen species.

When oxygen molecules absorb vacuum ultraviolet light having awavelength of 175 nm or less, the oxygen molecules are dissociated fromeach other and turn into singlet oxygen atoms and triplet oxygen atoms.Some oxygen atoms bond to oxygen molecules to form ozone molecules.Ozone molecules absorb vacuum ultraviolet light having a wavelength of175 nm or less and dissociate into singlet oxygen atoms and oxygenmolecules.

Thus, by irradiating spaces containing oxygen molecules with vacuumultraviolet light having a wavelength of 175 nm or less, singlet oxygenatoms are efficiently generated in the spaces. Accordingly, organicmolecules in surfaces of resins in contact with the spaces areeffectively oxidized and oxygen-containing hydrophilic functional groupsare generated in the surfaces. Note that such a phenomenon is caused,even when surfaces of resins are not irradiated with vacuum ultravioletlight, by irradiating spaces (immediately above the surfaces) in contactwith the surfaces with vacuum ultraviolet light. However, the phenomenonis more effectively caused by irradiating surfaces of resins with vacuumultraviolet light.

Next, the second phenomenon will be described.

The surfaces of resins have irregularities of a certain degree. The moreenhanced the flatness of resins by minimizing such irregularities, themore readily the resins can be joined together. When spaces containingoxygen molecules and being in contact with surfaces of the first andsecond resins are irradiated with vacuum ultraviolet light having awavelength of 175 nm or less, the surfaces of the first and secondresins in contact with the spaces are probably flattened. As a result ofsuch flattening of the surfaces, when the surfaces of the resins arebrought into contact with each other, the contact area between thesurfaces increases and the resins are probably firmly bonded together.For example, it has been demonstrated that, by irradiating a resinsubstrate having surface irregularities of about 40 nm (irregularitieshaving a height difference of about 40 nm) with vacuum ultravioletlight, the irregularities can be reduced to about 20 nm. In addition,when the surface of a cycloolefin polymer is irradiated with vacuumultraviolet light having a wavelength of 172 nm at an irradiationintensity of 10 mW/cm2 and a distance of 5 mm from a light source to thesurface of the resin, the state of the surface of the cycloolefinpolymer is observed with an atomic force microscope. As a result, it hasbeen demonstrated that the surface begins becoming gentle afterirradiation for 5 minutes; and the longer the irradiation time is, themore flat the surface becomes.

Next, the third phenomenon will be described. When spaces containingoxygen molecules and being in contact with surfaces of the first andsecond resins are irradiated with vacuum ultraviolet light having awavelength of 175 nm or less, organic molecules (polymers) in thesurfaces of the first and second resins, the surfaces being in contactwith the spaces, absorb the vacuum ultraviolet light and polymericchains are probably broken. As a result, the surfaces of the resins havelow molecular weight and the surfaces become soft. Thus, for example, byapplying forces in directions such that the surfaces of the resins arebrought into close contact with each other, the contact area between thesurfaces is probably increased. In addition, by making the surfaces havelow molecular weight, the surfaces become susceptible to thermaldeformation, which probably allows bonding at lower temperature.

According to the present invention, by irradiating surfaces of resinswith vacuum ultraviolet light having a wavelength of 175 nm or less, theabove-described three phenomena are probably induced in the surfaces ofthe resins. The resins can be probably bonded together firmly by thesynergistic effect of these three phenomena.

The irradiation with vacuum ultraviolet light in the step (I) can beperformed in a standard manner. In FIG. 1A, the irradiation of the firstresin 1 with the vacuum ultraviolet light 4 and the irradiation of thesecond resin 2 with the vacuum ultraviolet light 4 are performedsimultaneously. However, the irradiation of the resins may be performedseparately.

The light source will suffice as long as it can emit vacuum ultravioletlight having a wavelength of 175 nm or less and is not particularlyrestricted. For example, an excimer laser or an excimer lamp may beused.

In a bonding method according to the present invention, the irradiationintensity with vacuum ultraviolet light, the distance from a lightsource to surfaces of resins, and irradiation time are preferablyappropriately adjusted such that the reached light amount is 0.1 J/cm2or more and 10 J/cm2 or less. By making the reached light amount 0.1J/cm2 or more, the resins can be efficiently bonded together in a shortperiod of time. The more the reached light amount is, the more certainlythe resins can be efficiently bonded together. However, when the reachedlight amount exceeds 10 J/cm2, problems such as high fluorescence ofresins occur. Accordingly, the reached light amount is preferably made10 J/cm2 or less.

More preferably, the reached light amount is 1 J/cm2 or more. Byachieving such a reached light amount, a sufficiently large light amountof vacuum ultraviolet light reaches the surfaces of the first and secondresins. Thus, excitation (generation of active oxygen species, inparticular, singlet oxygen atoms, which have considerably highreactivity) of oxygen molecules is caused immediately above the surfacesof the first and second resins. As a result, the above-described threephenomena are effectively caused in the surfaces of the resins.Accordingly, the first resin and the second resin can be efficientlybonded together with more certainty with the surfaces serving as bondingsurfaces. Note that, even when the reached light amount is less than 1J/cm2 or is less than 0.1 J/cm2 (when vacuum ultraviolet lightsubstantially does not reach the surfaces of the first and secondresins), excitation of oxygen molecules is caused in spaces being incontact with the surfaces of the first and second resins and theabove-described three phenomena are caused in the surfaces. Thus, thefirst resin and the second resin can be bonded together. When thereached light amount is relatively small, for example, the bonding ispreferably performed by increasing the irradiation time with vacuumultraviolet light, increasing the temperature of the temperature rise inthe step (II), applying forces in directions such that the surfaces ofthe first resin and the second resin are brought into close contact witheach other upon the temperature rise, or the like.

For example, in the case of irradiation with vacuum ultraviolet lighthaving a wavelength of 172 nm at an irradiation intensity of 10 mW/cm2,for example, when the distance from a light source to a surface of aresin is made 5 mm and the irradiation is performed for 5 minutes, thevacuum ultraviolet light emitted from the light source attenuates toabout 30% thereof by reaching of the light to the surface of the resin.Thus, the reached light amount is 0.9 J/cm2. When the irradiation isperformed for 10 minutes under the same conditions, the reached lightamount can be made 1.8 J/cm2. In this way, the reached light amount canbe appropriately adjusted by appropriately adjusting the irradiationdistance or the irradiation time in accordance with, for example, theirradiation intensity with a light source used.

Spaces (spaces being in contact with surfaces of the first and secondresins) irradiated with vacuum ultraviolet light are spaces containingoxygen molecules such as the air. The partial pressure of oxygen in thespaces may be, for example, 10 to 105 Pa. As described above, byirradiating such spaces containing oxygen molecules with vacuumultraviolet light, surfaces of the first and second resins in contactwith the spaces are oxidized and functional groups containing oxygenatoms are generated in the surfaces.

The spaces irradiated with vacuum ultraviolet light have preferablyrelatively low humidity, for example, a humidity of 50% or less, morepreferably, 20% or less. This is because irradiation with vacuumultraviolet light under a high humidity environment takes time formaking surfaces of substrates hydrophilic and hence it may be difficultto bond resin substrates together by irradiation with vacuum ultravioletlight for a short period of time. In the case of irradiation with vacuumultraviolet light under a high humidity environment, as surfaces ofresin substrates are made hydrophilic, water vapor near the surfaces isadsorbed to the surfaces of the substrates and coatings of adsorbedwater are formed. These coatings absorb and react with active oxygen(atomic oxygen or ozone). As a result of this reaction, OH radicals aregenerated. Since OH radicals are less oxidative than atomic oxygen andozone, as a result, the rate of making a surface hydrophilic probablydecreases.

When irradiation with vacuum ultraviolet light is performed, the shapeof a surface irradiated may be controlled by a technique such asmasking.

The temperature rise in the step (II) may be performed by increasing thetemperature of the entirety of the first and second resins or byincreasing only the temperature of near-surface portions of the firstand second resins.

The means with which the temperature rise is performed is notparticularly restricted and a heater, a heating furnace, or the like maybe appropriately selected.

The temperature in the temperature rise is preferably, for example, atemperature at which the first resin and the second resin are notthermally fused and may be a temperature less than the glass transitiontemperatures of the first and second resins. A specific temperature inthe temperature rise is preferably appropriately determined inaccordance with the types of the first and second resins. For example,when the first and second resins are a cycloolefin polymer (ZEONEX(registered trademark) 330R manufactured by ZEON CORPORATION; glasstransition temperature: 123° C.) that will be described below inEXAMPLES, the temperature in the temperature rise may be made about 80°C. to 120° C.

In the step (II), as illustrated in FIG. 6, while forces 5 are appliedin directions such that the irradiation surface (surface 3 a) of thefirst resin 1 and the irradiation surface (surface 3 b) of the secondresin 2 are brought into close contact with each other, the temperatureof the irradiation surfaces may be increased. It is generally difficultto make surfaces of resins complete flat and surfaces of resinsubstrates generally have warps or the like. Accordingly, by performingthe temperature rise under the application of the forces in thedirections, the first resin and the second resin can be bonded togetherwith more certainty.

The magnitude of the forces applied in the directions may beappropriately determined in accordance with the shape of the first andsecond resins, in particular, the shape of bonding surfaces of theresins.

In a bonding method according to the present invention, at least oneresin selected from the first and second resins may be opticallytransparent. In a bonding method according to the present invention, thefirst resin and the second resin can be bonded together without usingorganic solvents or resin compositions. Accordingly, even when at leastone of the resins is optically transparent, the degradation of theoptical transparency of the resins caused by bonding can be suppressed.Note that optically transparent resins are generally amorphous resins.

In a bonding method according to the present invention, the first andsecond resins may be resins including, in the main chains, bonds betweencarbon and at least one element selected from carbon, oxygen, andnitrogen. As described above, in the method according to JapaneseUnexamined Patent Application Publication No. 2005-257283, one substrateneeds to be a substrate of polydimethylsiloxane (PDMS) having a mainchain constituted by Si—O bonds and having high affinity for siliconoxide films. In contrast, in a bonding method according to the presentinvention, resins including, in the main chains, bonds between carbonand at least one element selected from carbon, oxygen, and nitrogen canbe bonded together; and resins in which the main chains are constitutedby such bonds can also be bonded together.

In a bonding method according to the present invention, the first andsecond resins may be resins other than silicone resins. As describedabove, in the method according to Japanese Unexamined Patent ApplicationPublication No. 2005-257283, one substrate needs to be a substrate ofPDMS, which is one type of silicone resins. In contrast, according to abonding method of the present invention, resins other than siliconeresins can be bonded together.

In a bonding method according to the present invention, at least oneresin selected from the first and second resins may be at least oneselected from cycloolefin polymers and polycarbonate. In particular,since cycloolefin polymers have low adhesion to cycloolefin polymers orother resins due to the molecular structures of cycloolefin polymers, itis difficult to bond cycloolefin polymers by using an adhesive or thelike. Use of a bonding method according to the present invention enablesbonding of such cycloolefin polymers.

Specific structures of cycloolefin polymers are not particularlyrestricted. For example, bicyclic cycloolefin polymers such asnorbornenes may be used. Bicyclic cycloolefin polymers are generallyamorphous polymers and have excellent characteristics such as opticaltransparency, low birefringence, high heat resistance, and lowhygroscopicity. In recent years, bicyclic cycloolefin polymers have beenwidely used for applications such as optical parts.

In a bonding method according to the present invention, the first andsecond resins may be identical. Specifically, cycloolefin polymers canbe bonded together by a bonding method according to the presentinvention.

The first and second resins bonded together by a bonding methodaccording to the present invention are bonded at high strength. It isdifficult to manually separate resins bonded together by a bondingmethod according to the present invention. For example, when a tensileshear force is applied to resins bonded together with a tensile sheartesting apparatus until the resins are separated from each other, theresins are not separated at the bonding surfaces and fracture of thebase members (fracture of resins) are caused. Such high bonding strengthis achieved.

By a method for bonding resins according to the present invention, theabove-described high bonding strength can be achieved and resins bondedtogether can also be readily separated at the bonding surfaces anddisassembled by using a liquid at 40° C. or more, preferably 70° C. ormore, the liquid being selected from water and alcohol. For example, theentirety of bonded resins may be immersed in water at 40° C. or more sothat such a liquid is fed to the bonded portions. The reason why resinsbonded together by a bonding method according to the present inventioncan be readily separated from each other by using water at 40° C. ormore or the like is not clearly known. However, as described as thefirst phenomenon, since the bonding surfaces have high hydrophilicity,the reason is probably that water molecules and alcohol molecules canreadily reach the bonding surfaces. Alternatively, water whose pH ischanged by addition of acid or base can also be probably used. Even whena liquid such as water less than 40° C. (for example, water at roomtemperature (20° C.)) is used, resins can be separated from each otherby ultrasonic vibrations. Note that, to facilitate disassembly, withwater or the like, of the first and second resin substrates that arejoined, a configuration in which molecules of water or the like readilyreach the bonding surfaces may be employed. For example, tointentionally leave irregularities to a certain degree for easyseparation, vacuum ultraviolet light used for irradiation may beappropriately adjusted so that surfaces of resins are not made too flat.For example, when such surface irregularities have a height differenceof about 20 to 40 nm, high adhesion is achieved and disassembly usingwater or the like is also readily performed. When surface irregularitiesof a substrate are considered as waves, the balance between adhesion andease of disassembly can also be adjusted by adjusting the period of thewaves. For example, when the irregularities have a period of about 10 nmto 1 μm, the balance between adhesion and ease of disassembly can behighly achieved.

In a method for producing a resin article according to the presentinvention, resin portions of two or more parts included in the articleshould be bonded together by a bonding method according to the presentinvention.

Specifically, spaces containing oxygen molecules and being in contactwith surfaces of first and second resin portions, the surfaces servingas bonding surfaces, are irradiated with vacuum ultraviolet light havinga wavelength of 175 nm or less. After the irradiation, the surfaces aresubjected to temperature rise while the surfaces are in contact witheach other. Thus, the first resin portion and the second resin portionare bonded together with the surfaces serving as bonding surfaces.

The type of parts including resin portions, the parts being included inresin articles, is not particularly restricted. In addition, the type ofresins forming such resin portions may be similar to that of theabove-described first and second resins. Specifically, such a resin maybe at least one selected from cycloolefin polymers and polycarbonate.

As described above, resins bonded by a bonding method according to thepresent invention can be readily separated at the bonding surfaces byusing water or alcohol at 40° C. or more, preferably 70° C. or more; orby using a liquid less than 40° C. and ultrasonic vibrations.Accordingly, in a resin article produced by a method for producing aresin article according to the present invention, resin portions ofparts are bonded together such that the resin portions can be separatedfrom each other by using at least one liquid at 40° C. or more selectedfrom water and alcohol or by using a liquid less than 40° C. andultrasonic vibrations.

In a case where a resin article is a microchip in a method for producinga resin article according to the present invention, that is, in a methodfor producing a microchip according to the present invention, a pair ofresin substrates (a first resin substrate 11 and a second resinsubstrate 12) in which microchannels are formed at least one of thesubstrates illustrated in FIG. 7 as an example should be bonded togetherby a bonding method according to the present invention. Note that, inthe example illustrated in FIG. 7, channels 13 are formed in the firstresin substrate 11; and a surface 14 of the first resin substrate 11 inwhich the channels 13 are formed and a surface 15 of the second resinsubstrate 12 are bonded together to form a microchip 16 including thechannels 13.

Specifically, spaces containing oxygen molecules and being in contactwith surfaces of the first and second resin substrates, the surfacesserving as bonding surfaces, are irradiated with vacuum ultravioletlight having a wavelength of 175 nm or less. After the irradiation, thesurfaces are subjected to temperature rise while the first and secondresin substrates are placed to face each other and the surfaces are incontact with each other. Thus, the first resin substrate and the secondresin substrate are bonded together with the surfaces serving as bondingsurfaces.

The shape, size, and the like of such resin substrates are notparticularly restricted as long as channels are formed at least in oneof the substrates. As illustrated in FIG. 7, the channels may be formedin the bonding surface of a resin substrate.

In a method for producing a microchip according to the presentinvention, when channels are formed in an irradiation surface of a resinsubstrate, these channels may be irradiated with ultraviolet light. Thehydrophilicity of walls of channels can be enhanced by irradiation withultraviolet light depending on the type of a resin forming a substrate.As for whether channels are irradiated with ultraviolet light or not, astandard technique such as masking can be used.

In a method for producing a microchip according to the presentinvention, organic solvents and resin compositions do not remain on thebonding surfaces of resin substrates. Accordingly, microchips havingexcellent optical characteristics can be produced. For example, when anoptical detection is performed in an application of such chips, opticalcorrection conducted in the detection can be reduced.

As described above, resins bonded together by a bonding method accordingto the present invention can be readily separated at the bondingsurfaces by using water or alcohol at 40° C. or more, preferably 70° C.or more; or by using a liquid less than 40° C. and ultrasonicvibrations. Accordingly, in a microchip produced by a method forproducing a microchip according to the present invention, resinsubstrates are bonded together such that the resin substrates can beseparated from each other by using at least one liquid at 40° C. or moreselected from water and alcohol or by using a liquid less than 40° C.and ultrasonic vibrations.

Resin articles to which a production method according to the presentinvention can be applied are, in addition to microchips, for example,optical parts such as resin lenses.

It has been difficult to produce optical parts such as resin lenses bybonding resin parts together. When bonding by thermal fusion isperformed, produced resin lenses have distortion and have degradedoptical characteristics. When bonding with an organic solvent or a resincomposition is performed, coating of such a substance remains at thebonding surfaces, which degrades optical characteristics.

In contrast, by a method for producing a resin article according to thepresent invention, resin parts constituting a resin lens can be bondedtogether at a temperature lower than in bonding by thermal fusion andorganic solvents and resin compositions do not remain at the bondingsurfaces. Thus, degradation of optical characteristics of producedlenses can be suppressed. In addition, such combination of two or moreresin parts allows production of optical parts having complicated shapesthat have been difficult to produce.

EXAMPLES

Hereinafter, the present invention will be described in further detailusing EXAMPLES. The present invention is not restricted to EXAMPLESdescribed below.

Example 1

Surfaces of a pair of resin substrates (70 mm×20 mm, thickness: 2 mm)composed of a cycloolefin polymer (ZEONEX (registered trademark) 330Rmanufactured by ZEON CORPORATION; glass transition temperature: 123° C.)were irradiated with vacuum ultraviolet light (wavelength: 172 nm) froma Xe excimer lamp (UER20-172A manufactured by USHIO INC.). Theirradiation with the ultraviolet light was performed in the air. Thedistance between the lamp and the surfaces of the substrates was made 5mm or 30 mm. The irradiation intensity was made 10 mW/cm2. In the casewhere the irradiation distance was 5 mm, the irradiation time was made 5minutes or 10 minutes. In the case where the irradiation distance was 30mm, the irradiation time was made 10 minutes or 40 minutes. The vacuumultraviolet light was radiated to the entirety of a main surface of eachsubstrate.

The substrates having been irradiated with ultraviolet light were thenfaced to each other such that the irradiated surfaces were in contactwith each other. While forces were applied at a pressure of 0.7 MPa indirections such that the irradiated surfaces were brought into closecontact with each other, the temperature of the entire substrates wereincreased to 100° C. and this state was maintained for an hour.

Then, after the entire substrates were allowed to cool to roomtemperature, the forces were removed and the substrates were inspectedto determine whether the substrates were bonded together. For thesubstrates obtained at the irradiation distance of 5 mm, the substrateswere firmly bonded together in the cases of the irradiation time of 5minutes and 10 minutes and were not separated from each other withoutbeing fractured. For the substrates obtained at the irradiation distanceof 30 mm, bonding was insufficient in the case of the irradiation timeof 10 minutes whereas the substrates were firmly bonded together in thecase of the irradiation time of 40 minutes.

The above-described results show that, resins can be readily bondedtogether in the case of the irradiation distance of 5 mm in whichreached light amount is in the range of 0.1 J/cm2 to 10 J/cm2 even whenthe irradiation time is short. It has also been demonstrated that, evenin the case of the irradiation distance of 30 mm in which reached lightamount is smaller than the above case and only the spaces being incontact with substrate surfaces are seen to be substantially irradiatedwith vacuum ultraviolet light (the substrate surfaces are notsubstantially irradiated with vacuum ultraviolet light), resins can bebonded together by increasing the irradiation time.

Here, to inspect the state of the substrate surfaces having beenirradiated with vacuum ultraviolet light, the substrate surfaces inwhich the irradiation distance was 5 mm or 30 mm and the irradiationtime was changed in the range of 0 to 40 minutes were measured in termsof water contact angle with an automatic contact angle meter (DM500manufactured by Kyowa Interface Science Co., Ltd.). Furthermore, thesubstrate surfaces were also subjected to an XPS measurement. For thecases of the irradiation distance of 5 mm, the results in terms of watercontact angle are illustrated in FIG. 8 and the results of the XPSmeasurement are illustrated in FIG. 9. For the cases of the irradiationdistance of 30 mm, the results in terms of water contact angle areillustrated in FIG. 10 and the results of the XPS measurement areillustrated in FIG. 11. These results show that, the longer the time forwhich irradiation with vacuum ultraviolet light is performed becomes(the more the light amount of vacuum ultraviolet light reaching asubstrate surface becomes), the considerably less the contact anglebecomes and the more enhanced the hydrophilicity of the substratesurface becomes. The ratios of oxygen atoms to carbon atoms calculatedfrom the results of the XPS measurement illustrated in FIGS. 9 and 11show that, the longer the time for which irradiation with vacuumultraviolet light is performed becomes (the more the light amount ofvacuum ultraviolet light reaching a substrate surface becomes), theconsiderably more oxygen atoms increase.

Example 2

Surfaces of a pair of resin substrates (70 mm×20 mm, thickness: 2 mm)composed of a cycloolefin polymer (ZEONEX (registered trademark) 330Rmanufactured by ZEON CORPORATION; glass transition temperature: 123° C.)were irradiated with vacuum ultraviolet light (wavelength: 172 nm) froma Xe excimer lamp (UER20-172A manufactured by USHIO INC.). Theirradiation with the vacuum ultraviolet light was performed in the air.The distance between the lamp and the surfaces of the substrates wasmade 5 mm. The irradiation intensity was made 10 mW/cm2. The irradiationtime was made 5 minutes or 10 minutes. The vacuum ultraviolet light wasradiated to the entirety of a main surface of each substrate. Note that,when the distance between the lamp and the surfaces of the substrateswas made 5 mm, the light amount of vacuum ultraviolet light reaching asubstrate surface per second is 3 mJ/cm2·s. Accordingly, the reachedlight amount in the cases of the irradiation time of 5 minutes was 0.9J/cm2. The reached light amount in the cases of the irradiation time of10 minutes was 1.8 J/cm2.

Next, the substrates having been irradiated with vacuum ultravioletlight were faced to each other such that the irradiated surfaces were incontact with each other. While forces (pressure) were applied indirections such that the irradiated surfaces were brought into closecontact with each other, the entire substrates were subjected totemperature rise and this state was maintained. The pressure, thetemperature of the temperature rise, and the maintaining time werevaried. The results obtained by inspecting bonding states are shown inTable 1 and Table 2. Note that, in the Tables, cases in which thebonding state was good were denoted by “Good” and cases in which thebonding state was poor were denoted by “Poor”. The good bonding staterefers to a state in which substrates are not manually separated at thebonding surfaces and application of a tensile shear force until thesubstrates are separated from each other causes fracture of thesubstrates themselves. The poor bonding state refers to a state in whichsubstrates are manually readily separated at the bonding surfaces.

TABLE 1 0.3 MPa 0.4 MPa 0.5 MPa 0.6 MPa Time Temper- 30 1 3 5 30 1 3 530 1 3 5 30 1 3 5 ature s min min min s min min min s min min min s minmin min 50° C. Poor Poor Poor Poor Poor Poor Poor Poor Poor Poor PoorPoor Poor Poor Poor Poor 60° C. Poor Poor Poor Poor Poor Poor Poor PoorPoor Poor Poor Poor Poor Poor Poor Poor 70° C. Poor Poor Poor Poor PoorPoor Poor Poor Poor Poor Poor Poor Poor Poor Poor Poor 80° C. Poor PoorGood Good Poor Poor Good Good Poor Poor Good Good Poor Poor Good Good90° C. Poor Poor Good Good Poor Good Good Good Poor Good Good Good GoodGood Good Good 100° C.  Good Good Good Good Good Good Good Good GoodGood Good Good Good Good Good Good

TABLE 2 0.3 MPa 0.4 MPa 0.5 MPa 0.6 MPa Time Temper- 30 1 3 5 30 1 3 530 1 3 5 30 1 3 5 ature s min min min s min min min s min min min s minmin min 50° C. Poor Poor Poor Poor Poor Poor Poor Poor Poor Poor PoorPoor Poor Poor Poor Poor 60° C. Poor Poor Poor Poor Poor Poor Poor PoorPoor Poor Poor Poor Poor Poor Poor Poor 70° C. Poor Poor Poor Poor PoorPoor Poor Poor Poor Poor Poor Poor Poor Poor Poor Poor 80° C. Poor PoorGood Good Poor Poor Good Good Poor Poor Good Good Poor Poor Good Good90° C. Poor Poor Good Good Good Good Good Good Good Good Good Good GoodGood Good Good 100° C.  Good Good Good Good Good Good Good Good GoodGood Good Good Good Good Good Good

These results show that, in the cases of the irradiation time of 10minutes in which the reached light amount exceeds 1 J/cm2, conditions interms of temperature and pressure required for bonding are loosened.

Example 3

Surfaces of a pair of resin substrates (70 mm×20 mm, thickness: 2 mm)composed of a cycloolefin polymer (ZEONEX (registered trademark) 330Rmanufactured by ZEON CORPORATION; glass transition temperature: 123° C.)were irradiated with vacuum ultraviolet light (wavelength: 172 nm) froma Xe excimer lamp (UER20-172A manufactured by USHIO INC.). Theirradiation with the ultraviolet light was performed in the air. Thedistance between the lamp and the surfaces of the substrates was made 5mm. The irradiation intensity was made 10 mW/cm². The irradiation timewas made 5 minutes. The vacuum ultraviolet light was radiated to theentirety of a main surface of each substrate.

The substrates having been irradiated with ultraviolet light were thenfaced to each other such that the irradiated surfaces were in contactwith each other. While forces were applied at a pressure of 0.7 MPa indirections such that the irradiated surfaces were brought into closecontact with each other, the temperature of the entire substrates wasincreased to 100° C. and this state was maintained for 5 minutes.

Then, after the entire substrates were allowed to cool to roomtemperature, the forces were removed and the substrates were inspectedto determine whether the substrates were bonded together. The substrateswere firmly bonded together.

Five samples in a state in which resin substrates were bonded togetherby the above-described method were prepared. The samples were immersedin water at 5° C., room temperature (18° C.), 40° C., 60° C., and 90° C.and maintained in the water. The samples had a size of 8 mm×8 mm. Theresults are shown in Table 3.

TABLE 3 The measurement was performed with square samples of 8 mm perside. Room temperature 5° C. (18° C.) 40° C. 60° C. 90° C. No NoSeparated Separated Separated separation separation within within within5 minutes 5 minutes 5 minutes

For the samples having been immersed in water at 5° C. and in water atroom temperature, separation of the resin substrates was not caused. Incontrast, for the samples having been immersed in water at 40° C., 60°C., and 90° C., the resin substrates were separated at the bondingsurfaces and disassembled into two resin substrates.

By additionally applying a physical impact such as ultrasonic waves tothe above-described samples, the disassembly into two resin substrateswas rapidly achieved.

It was also demonstrated that, when samples similar to theabove-described samples were immersed in boiling ethanol at 78° C., thesamples were separated in 20 minutes.

The above-described results show that a resin article formed by bondingresin parts (resin substrates in this EXAMPLE) together by a bondingmethod according to the present invention can be disassembled with hotwater at 90° C. without fracturing the resin parts.

Example 4

Surfaces of a pair of resin substrates (70 mm×26 mm, thickness: 1 mm)composed of a cycloolefin polymer (ZEONEX (registered trademark) 330Rmanufactured by ZEON CORPORATION; glass transition temperature: 123° C.)were irradiated with vacuum ultraviolet light (wavelength: 172 nm) froma Xe excimer lamp (UER20-172A manufactured by USHIO INC.). Theirradiation with the ultraviolet light was performed in the air. Thedistance between the lamp and the surfaces of the substrates was made 5mm. The irradiation intensity was made 10 mW/cm2. The irradiation timewas made 5 minutes. The vacuum ultraviolet light was radiated to theentirety of a main surface of each substrate.

The substrates having been irradiated with ultraviolet light were thenfaced to each other such that the irradiated surfaces were in contactwith each other (the joining area became 26 mm×26 mm). While forces wereapplied at a pressure of 0.15 MPa in directions such that the irradiatedsurfaces were brought into close contact with each other, thetemperature of the entire substrates was increased to 100° C. and thisstate was maintained for 5 minutes.

Then, after the entire substrates were allowed to cool to roomtemperature, the forces were removed and the substrates were inspectedto determine whether the substrates were bonded together. The substrateswere firmly bonded together.

Samples in a state in which resin substrates were bonded together by theabove-described method were immersed in water at room temperature (20°C.) and maintained in the water. The samples did not separate even afterthe immersion for an hour.

Then, similar samples were immersed in water at room temperature andalso subjected to ultrasonic vibrations. The ultrasonic vibrations wereperformed with an ultrasonic cleaning apparatus (Model: “US-102”)manufactured by SND Co., Ltd. at a high frequency output of 100 W and ata vibration frequency of 38 kHz. As a result, the resin substrates wereseparated in 36 minutes.

Example 5

In EXAMPLE 5, the influence of the humidity of an atmosphere in theirradiation with vacuum ultraviolet light on bonding of resins in amethod for bonding resins according to the present invention wasstudied.

Surfaces of resin substrates (26 mm×76 mm, thickness: 1 mm) composed ofa cycloolefin polymer (ZEONEX (registered trademark) 480R manufacturedby ZEON CORPORATION; glass transition temperature: 138° C.) wereirradiated with vacuum ultraviolet light (wavelength: 172 nm) from a Xeexcimer lamp (UER20-172A manufactured by USHIO INC.). The distancebetween the lamp and the surfaces of the substrates was made 5 mm. Theirradiation intensity was made 10 mW/cm2. The vacuum ultraviolet lightwas radiated to the entirety of a main surface of each substrate.

The substrates having been irradiated with ultraviolet light were thenfaced to each other such that the irradiated surfaces were in contactwith each other. While forces were applied at a pressure of 0.5 MPa indirections such that the irradiated surfaces were brought into closecontact with each other, the temperature of the entire substrates wasincreased to 80° C. and this state was maintained for 5 minutes. Thus, apair of resin substrates was bonded together.

In this EXAMPLE, the humidity of an atmosphere in the irradiation withvacuum ultraviolet light was made 0.1% (use of dry air only) or 70%. Thestate of substrate surfaces irradiated with vacuum ultraviolet light atvarying irradiation times of 0, 5, 10, 20, 40, and 60 minutes athumidity of 0.1% and 70% was inspected. The inspection of the state ofthe substrate surfaces was performed by the measurement of water contactangle and XPS measurement as in EXAMPLE 1. The results in terms of watercontact angle are illustrated in FIG. 12. The results of the XPSmeasurement are illustrated in FIG. 13. The results illustrated in FIG.12 show that there was no difference between the final water contactangles at a humidity of 0.1% and at a humidity of 70% at the irradiationtime of 60 minutes with vacuum ultraviolet light; however, in themidstream stage (the irradiation time of 10 to 40 minutes with vacuumultraviolet light), the water contact angle at a humidity of 0.1% waslarger than that at a humidity of 70%. That is, the rate of making asubstrate surface hydrophilic was larger at the lower humidity. Inaddition, the ratio (O1s/C1s) of oxygen atoms to carbon atoms calculatedfrom the results of the XPS measurement illustrated in FIG. 13 showsthat, during the irradiation time of 0 to 40 minutes with vacuumultraviolet light, oxygen atoms considerably increase at a humidity of0.1% compared with at a humidity of 70%. This result shows that, at lowhumidity, more oxygen-containing hydrophilic functional groups areprobably generated on a substrate surface by irradiation with vacuumultraviolet light for a short period of time.

Furthermore, the bonding strength of pairs of resin substrates havingbeen bonded at humidity of 0.1% and 70% with the irradiation times of 5,10, 20, 40, and 60 minutes was evaluated. The bend strength of thebonded resin substrates was measured to evaluate the bonding strength.The measurement method of the bend strength was as follows: plate-shapedsamples of 76 mm×26 mm×thickness 1 mm were joined to form a cruciform(joined area: 26×26 mm2). A force was vertically applied from above tothe center of the joined portion to bend the sample. At this time, theindentation strength was measured with a load cell to evaluate thebonding strength. The measurement results are shown in Table 4.

TABLE 4 Humidity 0.1% Humidity 70 ± 2% Irradiation time Irradiation timewith vacuum with vacuum ultraviolet light Bend strength ultravioletlight Bend strength (min) (N/cm²) (min) (N/cm²) 5 Not measurable 5 Notmeasurable 10 0.5 10 Not measurable 20 1 20 0.5 40 4 40 4 60 4 60 4

These results show that resins can be bonded together by irradiationwith ultraviolet light for a short period of time at a humidity of 0.1%compared with at a humidity of 70%.

Comparative Example 1

As COMPARATIVE EXAMPLE 1, an example in which resin substrates wereirradiated with vacuum ultraviolet light in an atmosphere containing nooxygen molecules and the state of the resin surfaces was inspected willbe described.

Surfaces of resin substrates (26 mm×76 mm, thickness: 1 mm) composed ofa cycloolefin polymer (ZEONEX (registered trademark) 480R manufacturedby ZEON CORPORATION; glass transition temperature: 138° C.) wereirradiated with vacuum ultraviolet light (wavelength: 172 nm) from a Xeexcimer lamp (UER20-172A manufactured by USHIO INC.). The distancebetween the lamp and the surfaces of the substrates was made 5 mm. Theirradiation intensity was made 10 mW/cm2. The vacuum ultraviolet lightwas radiated to the entirety of a main surface of each substrate. Inthis COMPARATIVE EXAMPLE, the resin substrates were irradiated withvacuum ultraviolet light in an atmosphere containing no oxygen moleculesby purging the air with nitrogen gas. At this time, the humidity was1±1%.

In this COMPARATIVE EXAMPLE, the state of substrate surfaces having beenirradiated with vacuum ultraviolet light for varying irradiation timesof 0, 5, 10, 20, 40, and 60 minutes was inspected. The inspection of thestate of substrate surfaces was performed with the results in terms ofwater contact angle, FT-IR measurement, and XPS measurement. Themeasurement results of water contact angle are shown in Table 5. Theresults by FT-IR are illustrated in FIG. 14. The measurement results byXPS are illustrated in FIGS. 15 and 16. Atomic percent of oxygen atomsand carbon atoms calculated from the results by the XPS measurement areshown in Table 6.

TABLE 5 Irradiation time with vacuum ultraviolet light (min) Watercontact angle 0 99° 5 85° 10 79° 20 60° 40 48° 60 46°

TABLE 6 Irradiation time with vacuum ultraviolet light Atom % (min) O C5 11.20 88.80 10 17.30 82.70 20 19.01 80.99 40 20.65 79.35 60 21.0178.99

The results of water contact angles show that, even when irradiationwith vacuum ultraviolet light for 60 minutes is performed, the watercontact angle is 46° and the substrate surface is not sufficiently madehydrophilic. The results by FT-IR show that irradiation with vacuumultraviolet light does not cause a considerable increase in the amountof O—H groups and C═O groups in the surfaces of the resins. Note that aslight increase is probably caused by the influence of oxygen or watervapor present in trace amounts in the atmosphere. The results by XPSillustrated in FIGS. 15 and 16 also show that an increase in oxygen anda decrease in carbon are caused by irradiation with vacuum ultravioletlight; however, this is probably caused by the influence of oxygen orwater vapor remaining in the atmosphere. The results in Table 6 alsoshow that the ratio of oxygen atoms to carbon atoms in this COMPARATIVEEXAMPLE is smaller than that of EXAMPLE 1 and oxidation of the substratesurfaces is insufficient.

Comparative Example 2

As COMPARATIVE EXAMPLE 2, an example in which bonding of resins wasattempted by irradiating resin substrates with vacuum ultraviolet lightin an atmosphere containing no oxygen molecules will be described.

Surfaces of resin substrates (26 mm×76 mm, thickness: 1 mm) composed ofa cycloolefin polymer (ZEONEX (registered trademark) 480R manufacturedby ZEON CORPORATION; glass transition temperature: 138° C.) wereirradiated with vacuum ultraviolet light (wavelength: 172 nm) from a Xeexcimer lamp (UER20-172A manufactured by USHIO INC.). The distancebetween the lamp and the surfaces of the substrates was made 5 mm. Theirradiation time was made 10 minutes. The irradiation intensity was made10 mW/cm2. The vacuum ultraviolet light was radiated to the entirety ofa main surface of each substrate. In this COMPARATIVE EXAMPLE, the resinsubstrates were irradiated with vacuum ultraviolet light in anatmosphere containing no oxygen molecules by purging the air withnitrogen gas. At this time, the humidity was 1±1%.

Next, the substrates having been irradiated with vacuum ultravioletlight were faced to each other such that the irradiated surfaces were incontact with each other. While forces (pressure) were applied indirections such that the irradiated surfaces were brought into closecontact with each other, the entire substrates were subjected totemperature rise and this state was maintained. The results obtained byinspecting bonding states in which the pressure, the temperature of thetemperature rise, and the maintaining time were changed are shown inTable 7. Note that, in the Table, cases in which the bonding state wasgood were denoted by “Good” and cases in which the bonding state waspoor were denoted by “Poor”. The good bonding state refers to a state inwhich substrates are not manually separated at the bonding surfaces andapplication of a tensile shear force until the substrates are separatedfrom each other causes fracture of the substrates themselves. The poorbonding state refers to a state in which substrates are manually readilyseparated at the bonding surfaces.

TABLE 7 0.4 MPa 0.5 MPa 0.7 MPa 0.8 MPa Time Temper- 30 1 3 5 30 1 3 530 1 3 5 30 1 3 5 ature s min min min s min min min s min min min s minmin min 80° C. Poor Poor Poor Poor Poor Poor Poor Poor Poor Poor PoorPoor Poor Poor Poor Poor 90° C. Poor Poor Poor Poor Poor Poor Poor PoorPoor Poor Poor Poor Poor Poor Poor Poor 100° C.  Poor Poor Poor PoorPoor Poor Poor Poor Poor Poor Poor Poor Poor Poor Poor Poor

As shown in Table 7, even when the temperature was increased to 100° C.and the pressure was increased to 0.8 MPa, good bonding was notachieved. These results show that bonding of resins require irradiationwith vacuum ultraviolet light in an atmosphere containing oxygen.

According to the present invention, a bonding method in which a resinand a resin can be bonded together with high productivity at atemperature lower than that in bonding by thermal fusion can beprovided. A bonding method according to the present invention can beapplied to methods for producing various resin articles, for example, itcan be applied to a method for producing a microchip. Furthermore,according to a bonding method of the present invention, since resinshaving been bonded together can be readily separated from each other,for example, recycling of resins is advantageously performed. Forexample, when a bonding method according to the present invention isapplied to medical microchips such as blood test chips, such microchipsafter use can be separated and disassembled and microchannel portionscan be washed. As a result, medical microchips after use can be disposedof not as medical waste but as general plastic waste.

1. A resin article comprising a plurality of parts including resinportions, the plurality of parts being bonded together through the resinportions, wherein the resin portions are bonded to each other by amethod for bonding a first resin and a second resin, the methodcomprising the steps of: (I) irradiating a space containing oxygenmolecules with vacuum ultraviolet light having a wavelength of 175 nm orsmaller, the space being adjacent to a first surface of the first resinand a second surface of the second resins; and (II) after theirradiating, placing the first surface and the second surface in contactwith each other, and increasing a temperature such that the first resinand the second resin are bonded to each other via the first and secondsurfaces serving as bonding surfaces.
 2. The resin article according toclaim 1, wherein in the method for bonding, the step (I) also irradiatesthe first surface and the second surface with the vacuum ultravioletlight.
 3. The resin article according to claim 2, wherein, in theirradiating, an amount of the vacuum ultraviolet light reaching thefirst and second surfaces is in a range from 0.1 J/cm² to 10 J/cm². 4.The resin article according to claim 3, wherein, in the irradiating, theamount of the vacuum ultraviolet light reaching the first and secondsurfaces is 1 J/cm² or greater.
 5. The resin article according to claim1, wherein, in the irradiating, a partial pressure of oxygen in thespace is 10 to 10⁵ Pa.
 6. The resin article according to claim 1,wherein the step (II) increases the temperature to a temperature lowerthan glass transition temperatures of the first and second resins. 7.The resin article according to claim 1, wherein the method the step (II)further comprises: applying a force in a direction such that the firstand second surfaces are pressed against each other while the temperatureis being increased.
 8. The resin article according to claim 1, whereinrespective main chains of the first and second resins include a bondbetween carbon and at least one element selected from carbon, oxygen,and nitrogen.
 9. The resin article according to claim 1, wherein atleast one of the first and second resins is selected from cycloolefinpolymers and polycarbonate.
 10. The resin article according to claim 9,wherein the at least one of the first and second resins is a bicycliccycloolefin polymer.
 11. The resin article according to claim 1, whereinthe first and second resins are of a same type.
 12. The resin articleaccording to claim 1, wherein the bonded resin portions are configuredto become separable from each other by applying at least one liquidselected from water and alcohol at a temperature of 40° C. or higher, orby applying the liquid at a temperature lower than 40° C. in combinationwith ultrasonic vibrations.
 13. The resin article according to claim 12,wherein the resin article includes an optical part or a resin lens. 14.The resin article according to claim 12, wherein the plurality of partsare a pair of resin substrates bonded to each other, at least one of theresin substrates including a microchannel.
 15. The resin articleaccording to claim 1, wherein in the step (II), the irradiating reducesirregularities of the first and second surfaces while maintainingcertain surface roughness of the first and second surfaces.
 16. Theresin article according to claim 15, wherein the certain surfaceroughness of the first and second surfaces allows the first and secondresins to become separable from each other if at least one liquidselected from water and alcohol at a temperature of 40° C. or greater isapplied, or the liquid at a temperature less than 40° C. in combinationwith ultrasonic vibrations is applied.
 17. The resin article accordingto claim 16, wherein a height difference of the irregularities isadjusted in a range of 20 to 40 nm by the irradiating.
 18. The resinarticle according to claim 1, wherein the resin article includes anoptical part or a resin lens.
 19. The resin article according to claim1, wherein the plurality of parts are a pair of resin substrates bondedto each other, at least one of the resin substrates including amicrochannel.